pv: A Python repository from blebo

pv - a Python-based PV inverter monitoring library

28 Jan 11

Introduction
============
pv provides a simple Python API to monitor and control some photovoltaic
inverters via serial connection.

pv was developed specifically for the Carbon Management Solutions CMS-2000
inverter, and is expected to work for the Solar Energy Australia Orion inverter
since they are essentially the same device with a different badge. The
communication protocol was based on examining the data exchange between the
inverter device and the official Pro Control 2.0.0.0 monitoring software for the
Orion inverter, and the SunEzy Control Software.

For more information, see http://pv.codeplex.com/


Getting Started
===============

This section will guide you through making the first communications with the
PV inverter connected via the computer's serial port.

Debugging
---------
For debugging purposes, the bytes sent and received via the serial port can be
printed on screen. Additionally, ANSI colouring can be enabled for colour coding
of different fields in each packet for readibility:
	import pv
	pv.debug()
	pv.debug_color()


Interfacing with CMS-2000
-------------------------
Communication with the solar inverter is over a serial interface. First, we need
to open the serial port to which the inverter is connected:
	import serial
	port = serial.Serial('/dev/ttyS0')
	port.open()

We then construct a CMS inverter object on this port:
	from pv import cms
	inv = cms.Inverter(port)

At this stage, the inverter does not represent a physical inverter, because we
do not know whether or not one is actually connected. To initialise this object
and associate it with an actual inverter:
	inv.reset()					# Reset all communications on the serial connection
	sn = inv.discover()			# Look for connected devices
	if sn is None:
		print "Inverter is not connected."
		sys.exit(1)
	ok = inv.register(sn)		# Associates the inverter and assigns default address
	if not ok:
		print "Inverter registration failed."
		sys.exit(1)

After registering the connected inverter, we can start querying it. For example,
to obtain an extended version string for the inverter:
	print inv.version()

Inverter parameters and status require a little more processing because the
query returns more than one field, and the values are packed into a binary
bitstream. First, we find out the layout in which the data that the inverter
sends to us is organised. Then, we take the data queried from the inverter, and
then use the layout information to interpret what it means:
	param_layout = inv.param_layout()
	parameters = inv.parameters(param_layout)
	for field in parameters:
		print "%-10s: %s" % field

	status_layout = inv.status_layout()
	status = inv.status(status_layout)
	for field in status:
		print "%-10s: %s" % field


PVOutput.org
------------
To interact with the PVOutput.org service, you must first create a connection to
PVOutput.org:
	from pv import pvoutput
	api_key = ''
	system_id = 123
	conn = pvoutput.Connection(api_key, system_id)

Next, interactions via the PVOutput.org API can be made via the methods of this
connection object:
	import time
	status = dict(status)
	conn.add_status(
			time.strftime('%Y%m%d'),
			time.strftime('%H:%M'),
			energy_exp=status['E-Total'],
			power_exp=status['Pac'],
			cumulative=True)
	print conn.get_status()
blebo/pv
